I have a large number of files I have to load and clean up in Calibre (100k+).

I'm doing this piecemeal, because if I try to add files past around 20k to a calibre library, it slows down enormously. So I'm wondering if it's possible to launch multiple copies of calibre (using different databases and library folders) so I can import into one while cleaning up the other. I've tried, but the second copy doesn't seem to launch.

I have a large number of files I have to load and clean up in Calibre (100k+).

I'm doing this piecemeal, because if I try to add files past around 20k to a calibre library, it slows down enormously. So I'm wondering if it's possible to launch multiple copies of calibre (using different databases and library folders) so I can import into one while cleaning up the other. I've tried, but the second copy doesn't seem to launch.

Win7, 8GB Memory, AMD x6.

Like Kovid says, only one instance of the Calibre GUI can run at a time. But what you want is possible using the command line tools ('calibredb add'), if you're importing into another library than the one the GUI is working on.

I've done that myself in the past (and the '--dont-notify-gui' switch, which you will need, came to be because of it ).

Doing More on the same system is just going to slow it down more.
Desktop PC's are typically I/O bound because of a single data and memory buses.
There is a reason that many Server class machines have 2 or more complete sets of CPU's, RAM, I/O

I suggest that your old friend KVM and a desk load of PC's will be faster.
In the end, Calibre can combine Libraries (Copy TO Library)